Musnad Ahmad 8:93

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Abu Ishaq, from al-'Aizar, from 'Umar ibn Sa'd, from his father Sa'd, from the Prophet, peace and blessings of Allah be upon him, that he said: "I am amazed at the Muslim; if good befalls him, he praises Allah and is grateful, and if a calamity befalls him, he seeks reward and is patient. The Muslim is rewarded for everything, even for the morsel he lifts to his mouth."